Development of neutron dark-field imaging technique with polychromatic neutron beam

Abstract

Grating-based neutron phase-contrast and dark-field imaging techniques based on phase shift and amplitude effects have been developed over the past few years which were used for some scientific applications such as bulk magnetic material and microstructure studies. Neutron dark-field imaging has been demonstrated to be able to visualize the magnetic domains of magnetic materials owing to a strong dark-field signal from magnetic domain walls. Moreover, a three-dimensional image of magnetic domain structures within the bulk of FeSi crystals can be obtained using neutron dark-field tomography. Although neutron darkfield imaging shows a great potential in investigating internal magnetic domain structures, improved image quality is demanded for more detailed information. The established neutron grating interferometers at some research facilities were designed for neutrons having wavelengths above 4.0Å , and are usually tested with monochromatic or quasi-monochromatic neutrons. The reason why monochromatic or quasi-monochromatic neutrons are used is because they provide better contrast sensitivity and thus make it easier to model the interference effect of the system. Monochromatic or quasi-monochromatic neutrons, however, do not provide not only enough number of neutrons for imaging with a high spatial resolution but also give fast data acquisition time. This limitation is mainly due to the large number of neutrons lost during the monochromatization process. Limited neutron flux and detector resolution are one of the main challenges in making a neutron grating interferometer as an efficient measurement technique. To achieve high resolution neutron image with a short data acquisition time, it is natural to adopt polychromatic neutron beam without monochromatization. It is important to find the neutron grating interferometer with a maximum visibility to effectively use a polychromatic thermal neutron beam. To maximize the visibility performance, a gratingbased interf...